Exam 1 Chapter 4 (Cells) Flashcards
When and by whom were cells discovered?
Robert Hooke in 1665
Which two people studied cells and came up with cell theory?
Mathias Schleiden (1838) and Theodor Schwann (1839).
What is the cell theory?
A cell is the smallest living unit of all living organisms. All living things are composed of one or more cells. Cells arise only by division of a previously existing cell.
What are the two types of microscopes?
Light and electron microscopes
Light: Uses magnifying lenses with visible light and resolves up to 200 nm; because the wavelength of light is larger than that of electrons, resolution is limited since resolution of a microscope cannot be more than 1/2 of the wavelength of light
Electron: uses beam of electrons and can resolve up to 0.2 nanometers apart
Give some examples of cells
Bacterium (1 micrometer), archaean, amoeba (100 um), algae, fungal cells, animal cells (10 um), plant cells
What are the two types of electron microscopy?
Transmission electron microscopy (TEM) (2D) and Scanning Electron Microscopy (3D).
Bright Field Microscopy
Light passes directly through the specimen, staining with a dye increases contrast in a specimen since many cell structures have insufficient contrast to be discerned. However, dyeing usually kills the cells (20 micrometers)
Fluorescence microscopy
Different molecules in cells stained with specific fluorescent dyes, which fluoresce when illuminated with UV light, and locations are seen by viewing the emitted visible light (10 um)
Triple labeled fluorescent microscopy
Three different fluorescent dyes are used simultaneously to label different structures (20 um)
Nomarski
Special lenses enhance differences in density, giving a 3D appearance
Confocal laser scanning microscopy
Lasers scan specimen in 3D, localizing fluorescence emitted from each point, and a computer reconstructs 3D image (10 um)
Super-resolution fluorescent microscopy
Precisely targeting laser light that stimulates fluorescence produces v high resolution. 10 nm
TEM
Beam of electrons is focused on a thin section of a specimen in a vacuum. Electrons that pass through form the image, structures that scatter electrons appear dark. TEM is used primarily to examine structures within cells. Various staining and fixing methods are used to highlight structures of interest. 500 nm
Scanning electron microscopy
A beam of electrons is scanned actoss a whole cell or organism, and the electrons excited on the specimen surface are converted to a 3D image. In the image, small raised dots are proteins in a cell membrane
Unit conversions of a meter
1 m= 10^2 cm, 10^3 mm, 10^6 micrometers, 10^9 nanometers
Up to what point can the human eye see?
1 mm- frog egg/fish egg
Light microscope range
1 mm-1 micrometer; human egg, plant cell, animal cell, mitochondrion, e coli
Electron microscope range
100 micrometers to 0.1 nanometers- large virus, ribosome, cell membrane thickness, dna diameter, h atom
Why is it beneficial for cells to be so microscopic?
higher surface area to volume ratio means there is enough surface area to accomodate all of the exchange needs for the cell’s volume. As diameter increases, ratio also decreases, meaning insufficient surface area is present
How do cells increase surface area?
Via extensions or folds
Describe the plasma membrane of a cell
Phospholipid bilayer with embedded protein molecules. It is hydrophobicbarrier to water-soluble substances, but selected substances can enter through transport protein channels
What are the components of the cytoplasm?
The cytosol (aqueous, contains ions, organic molecules, and organelles), and the cytoskeleton (maintains cell shape and aids in cell division and chromosome segregation)
What are prokaryotes?
Cells with no boundary membranes or internal membranes (bacteria and archaea)
What are eukaryotes?
Cells with an endomembrane system consisting of membrane bound organelles and a nucleus separated from cytosol
Glycocalyx
Polysaccharide-based cell wall in prokaryotes; if it is closely attached, it is a capsule and if it is loosely attached, it is a slime layer
What is special about the plasma membrane of the prokaryote?
It carries out a lot of the functions that organelles in eukaryotes do; for example it contains molecular systems that metabolize food molecules or light into ATP
What do prokaryotic cytoskeletons do?
Maintain cell shape and function in cell division?
Describe flagella
A long extension off of the cell membrane that rotates in a socket to facilitate movement
What are pili?
Small, hairlike extensions that attach the cell to other surfaces and other cells. A sex pilus joins bacteria during mating
What are the common shapes among prokaryotes?
Spherical, rodlike, and spiral
What is the DNA like for most prokaryotes?
Organized into a single circular molecule called the prokaryotic chromosome
How are proteins synthesized in prokaryotes?
Information from DNA is copied into mRNA and carried to ribosomes in cytoplasm, which assemble amino acids into proteins
What structures are present in animal cells but not plant cells?
Centrosomes with centrioles (roles in cell division)
Lysosomes (digestion)
Cilia (hairlike projections involved in locomotion)
Describe the process of cell fractionation
- Whole cells
- Whole cells broken down into fragments
- Fragments centrifuged at 500 g, which pellets nuclei
- Supernatant is taken and centrifuged at 20,000 g, which pellets mitochondria and chloroplasts
- Supernatant is taken again and centrifuged at 150,000 g, pelleting ribosomes, proteins, and nucleic acids
Present in plant but not animal cells
Cell wall (with plamodesmata)
Chloroplasts
Central vacuole
What is the nucleolus?
A region where ribosomal RNA is synthesized and ribosomal subunits are formed then exit through nuclar pores
How many nuclei in an eukaryotic cell?
1
How many bilayers and leaflets in nucleus?
2 bilayers and 4 leaflets
What is the protein that reinforces the nuclear envelope?
Lamins-intermediatefilament
What do nuclear pores do?
Control and regulate passage of molecules in and out
What is the structure of chromosomes in eukaryotes?
Linear; organized with its proteins into an eukaryotic chromosome
What is the liquid in the nucleus called?
nucleoplasm
Chromatin
A mix of dna and proteins found in the nucleus
True or false: ribosomes can be found on the outer surface of the nuclear envelope
True
True or false: there is a space between outer and inner nuclear membrane
True
Describe the structure of the nuclear pore complex
Basket like- control and regulate passage
Why is chromatin important?
It helps form chromosomes
Describe the experiment used to find the nuclear localization signal
Amino acid at position 128 was mutated from lysine to threonine, which made the mutated protein localize in the cytoplasm. This meant the amino acid was important for localizing the protein to the nucleus, and mutating other amino acids in same reion impaired import. Deleting amino acids 1-126 or 136-708 had no effect on proteins localizing in the nucleus so those amino acids are not important for nuclear localization. Deleting 127-133 caused the protein to localize to the cytoplasm, meaning this 7-acid sequence is a signal for nuclear localization
What are the subunits of ribosomes?
Large and small; composed of ribosomal RNA and proteins and assembled in the nucelolus
Where are ribosomes found?
Attached to membranes and free in cytosol; proteins made on free ribosomes may remain there, pass into nucleius, or become parts of mitochondria, chloroplasts, cytoskeleton, or other structures
What is the endomembrane system?
A series of membranes throughout the cytoplasm dividing the cell into compartments w/ different cellular functions- can be connected physically or via vesicles that transfer substances
What are the components of the endomembrane system?
Nuclear envolope, ER, golgi complex, lysosomes, vesicles, plasma membrane
Describe the structure of ER
consists of membranous channels and cisternae, which have hollow inside called the ER lumen
What is the rough ER?
Contains ribosomes on the surface that synthesize proteins using information from mrna (gene for protein is in nucleus, which is transcribed into mrna which exits the nucleus). This mrna is decoded in translation to make proteins, which then enter the ER lumen to fold into their final form; here, chemical modifications such as addition of carbs to make glycoproteins occur. Proteins are then delivered to other regions of the cell within small vesicles that pinch off from the ER; continuous with nucleus and smooth er
Smooth er
No ribosomes, synthesize lipids that become part of cell membranes and can also convert drugs, poisons, and toxic byproducts into substances that can be tolerated and more easily removed from the body
Golgi apparatus
Formed from golgi bodies (flattened sacs of interconnected membranes); made of cis-golgi network, cis, medial, trans golgi, and trans-golgi netwrok. Proteins enter in on cis-face through vesicles that fuse with the membrane and modified proteins exit through trans face in vesicles that bud off
Function of golgi
Collects, packages, distributes molecues synthesized in one area and needed in another through vesicles
Sugar production and addition to form glycolipids and glycoproteins, final protein folding, and storage of secreted material
How is the cis golgi network formed?
Fusion of transport vesicles from ER; conversely, trans golgi breaks down into vesicles with fully modified proteins
Exocytosis
Membrane of vesicle fuses with plasma membrane and BECOMES A PART OF IT
What are lysozomes?
Digestive vesicles emerging from trans golgi network; found only in animals. Enzymes break down macromolecules and use subunits in other areas- destroys engulfed foreign matter (phagocytosis) and worn out organelles (autophagy). Fuse with endocytic vesicles–becomes.continuous
What are phago and pinocytosis?
Phagocytosis involves cell engulfing insoluble material, pinocytosis involves engulfing soluble material; both involved with lysozymes
Why is the ph of lysozymes lower?
Allows for digestion
Describe the secretory pathway
genes transcribed into mrna which exits nucleus and attaches to ribosomes for translation into protein; enter er and become modified , veiscles bud off and enter golgi where modificatin and delivery occurs and vesicles transport and some store; lysosomes also come from golgi and digest endocytic vesicles
Peroxisomes
Enzyme-bearing, membrane enclosed vesicles that oxidize fatty acids; h2o2 is broken down by catalase present in peroxisomes
Mitochondria
2 bilayers (outer and inner) inner is folded up into cristae, and innermost complex is matrix where DNA, ribosomes, other components; cellular respiration occurs in cristae and matrix where food is broken down and turned into ATP; requires oxygen for cellular respiration
Chloroplasts
Enclosed internal compartments of stacked grana containing thykaloids; found in photosynthetic organisms
Describe the evolutionary origin of mitochondria
1.5 billion years ago- ancient eukaryote ingested ancient aerobic prokaryote, forming endosymbiotic mutualistic relationship where one cannot live without the other. Same thing happened 1 bya with plants. Mitochondria have their own DNA and rna resembling bacterial structures
Cytoskeleton
Interconnected system of protein fibers and tubes extending throughout the cytoplasm ; maintains cell shape, internal organization, and functions in movement; conrains microtubules, intermediate filaments, and microfilaments
Actin filaments
Aka microfilaments; 5-7 nm, directs changes in cell shape and direction of movement. Determines locations of membrane bound organelles in plant cells and forms crosslinks with other filaments. Provides tracks for intracellular transport and interacts with myosins to generate forces like muscle contractions. Assembled from 2 actin subunit chains wound around in a helical spiral. They have polarity.
Where do actin/microfilaments grow more quickly?
Near the + end
Microtubules
Help determine cell shape and direction of organelles in animal cells; provides tracks for intracellular transport and moves and separates chromosomes during cell division. Also determines growth patterns of plant cell walls.
Structure of microtubules
Largest of the filaments at 25 nm diameter. Made of alpha and beta tubulin dimers (one alpha and one beta) added at the same time. Walls of microtubule have 13 protein filaments arranged side by side and dimers are added inti positive side head to tail. alpha is negative
What role do microtubules play
Change length by addition or removal of tubulin dimers (poymerization/depolymerization); microtubules radiating from centrosome anchor organelles in position and centrioles at midpoint of cell center are barrel shaped structures called centrioles. They provide tracks for vesicles to move to plasma membrane and they also move chromosomes.
How do cell movements occur?
Motor proteins push and pull against microtubules (dyenins and kinesins) or microfilaments (myosins)
Intermediate filaments
Assembled from large group of intermediate filament proteins; intermediate in size and occur singly, in bundles, and in interlinked networks with microtubules and microfilaments. They provide structural support and are tissue specific in protein composition. 8-12 nm and support nuclear envelope and found in animal cells.
Functions of microfilaments
Components of contractile elements in muscle fibers; also aid in cytoplasmic streaming, where nutrients, proteins, and organells are transported. It also helps with amoeboid movement and divides the cytoplasm when animal cells divide.
What do dyenins do?
Carry cargo from edge to cell body
Kinesins
opposite of dyenins, carry towards edge of cell
How do motor proteins work?
One end of a motor protein is fixed to something like a cell structure vesicle or a microtubule/microfilament; the other have reactive groups that walk along another microtubule or microfilament by attaching, swiveling, and releasing.
What are cilia and flagella?
Extensions rising from the surface of a cell. Prokaryotes and eukaryotes both have flagella, but only eukaryotes have cilia. Plants do not have flagella or cila.
Where do flagella and cilia arise from?
Centrioles that become part of the basal body of the cell.
Describe structure of flagella and cilia
Pair of 9 doublets with two more in the center of microtubules, creating a 9+2 complex
How is movement produced in the flagella and cilia?
Dynein arms branch between microtubules and slide the microtubules over eachother
List structures found in cross section of a flagellum
2 central microtubules, central sheath, spokes leading to microtubule pairs each connected to eachother via dynein and connective system links
Describe movement of flagella
S-shaped waves that travel from base to tip- such as found in sperm (10 micrometers)
Describe movement of cilia
Beat in an oarlike power stroke forward, then followed by a recovery stroke backwards
How are flagella and cilia able to move?
Dynein facilitates the microtubules doublets actually sliding over eachother, so doublets on the bending side extend farther
What structures are found in plants but not animals?
Chloroplasts, central vacuole, plant cell walls
Where else can chloroplasts and cell walls be found?
Chloroplasts are found in algal protists and cell walls are found in plant and fungi cells
What is the animal cell parallel to plastids?
Mitochondria
What are chloroplasts?
Yellow-green plastids
What are amyloplasts?
Plastids that store starch
Chromoplasts
Store colored pigments responsible for fall leaves and ripening fruits
What are some features of plastids?
They contain DNA genomes, molecular machinery for gene expression and the synthesis of proteins on ribosomes. They can encode their own proteins or can have some imported in
What is the structure of a chloroplast?
Surrounded by an outer boundary membrane and an inner boundary membrane, which both completely enclose the stroma (fluid interior). Inside the stroma is a third membrane system containing thylakoids- flattened sacs. They can be stacked to form grana
What is a special component of thylakoids in chloroplasts?
Membranes contain chlorophyll which converts light to chemical energy
What is the central vacuole?
Large vesicles performing specialized functions
How much of a plant cell’s volume may be occupied by the vacuole?
90%
What is the tonoplast?
The membrane of the central vacuole contains proteins that transport molecules in and out of the tonoplast
What functions do central vacuoles carry out?
Store salts, organic acids, sugars, storage proteins, pigments, and, in some cells, waste products.
Contain enzymes to break down macromolecules
Contain molecules that provide chemical defense
List the layers of cell wall
Plasma membrane
Secondary cell wall- additional layers of cellulose fibers and branched carbohydrates; in woody plants, reinforced by lignin
Primary cell wall- soft and flexible
How are adjacent cells held together?
A layer of polysaccharides (pectin) called the middle lamella
What are cell walls composed of?
Cellulose
Plasmodesmata
Plasma membrane-lined channels that connect cytosols of adjacent cells, which allows ions and molecules to continuously move from one cell to another
List the specialized structures that organize cells at three levels
Cell adhesion molecules- hold cells together
Cell junctions- seal spaces between cells and provide communication
ECM: supports and protects cells and provides mechanical linkages between tissues
Cell adhesion molecules
Glycoproteins in plasma membrane binding to molecules on other cells; make initial connections between cells early in embryonic development
How does cancer metastatize?
Adhesions such as those produced by cell adhesion molecules are lost, allowing cancer cells to break loose and migrate to new locations; bacteria and viruses also target these molecules
Anchoring junctions
Buttonlike spots or belts that run around cells to weld them together. Most common in tissues subject to mechanical forces
Demosomes
Anchoring junctions with intermediate filaments that anchor the junction in underlying cytoplasm
Adherens junctions
Microfilaments are anchoring cytoskeletal component
Tight junctions
Regions of tight connections between membranes of adjacent cells; seal spaces between cells in cell layers that cover internal organs, outer surface of body, and layers inside cavities and ducts. Formed by fusion of proteins of plasma membtanes of adjacent cells; complex and tight enough to prevent ion leaks.
Gap junctions
Open direct channels that allow ions and small molecules to pass directly from one cell to another. Hollow protein cylinders embedded in plasma membranes of adjacent cells line up and form a pipeline that connects cytoplasm of once cell with the cytoplasm of next. Gap junctions communicate between cells within a tissue such as heart muscle tissue
Extracellular matrix
consists of proteins and polysaccharides excreted by cells. Forms the mass of skin, bones, tendons, and highly specialized extracellular structures.
What does ECM affect
Cell division, adhesion, motility, embruyionic development, response to wounds and disease
What are the main components of ecm?
Glycoproteins (especially collagen in animals)
Fibronectins bind to collagen fibers (bind to integrins- receptor proteins) in plasma membrane, which bind to microfilaments in cytoskeleton
What determines the consistency of the matrix?
Proteoglycans surrounding collagen fibers- in bone, network has mineral crystals to form hard, dense, elastic material
